Heated plasmas are known to be useful for the generation of x-radiation and for the generation of neutrons through the nuclear fusion of light ions, typically hydrogen and its isotopes. There has been a great deal of recent interest in z-pinch and x-pinch techniques, in which a plasma is compressed under the influence of its own magnetic field, which leads to both temporary confinement and adiabatic heating of the plasma.
In particular, so-called “micropinch” techniques have been developed, in which a small puff of gas (i.e., a “micropuff”) is ionized and electromagnetically excited by a high-voltage pulse, typically of on the order of kilovolts in amplitude and microseconds in duration. The puff of gas is emitted from a nozzle that may be configured for subsonic, sonic, or supersonic gas emission. For example, nozzles of the converging-diverging, or Laval, design, among others, have been found useful for generating gas puffs at Mach numbers up to M=8 or more, while also being amenable to miniaturization.
For example, U.S. Pat. No. 8,530,854, which is commonly owned herewith, issued on Sep. 10, 2013 to M. S. Derzon et al. under the title “Micro Gas-Puff Based Source.” That patent discloses several approaches to the design of a plasma source that uses a micro-scale gas puff to generate neutrons, x-radiation, or other energetic particles. The source as described there has a diode configuration including an anode and a cathode and a reaction chamber included between them. A micro-electromechanical systems (MEMS) gas supply injects a puff of gas between the anode and the cathode within the chamber. A pulsed power supply applies the voltage between the electrodes that compresses the gas puff to form the plasma. In some implementations, the gas supply is adapted to create a quasispherical gas density profile, i.e. a profile that is cylindrically symmetrical but dependent on the azimuthal coordinate in such a way that when the power supply discharges, the puff will implode under its own magnetic field in a manner that tends to concentrate the heating effect near its center. The entirety of U.S. Pat. No. 8,530,854 is hereby incorporated herein by reference.
In the field of medical imaging, it has long been conventional to generate x-rays by the beam-on-target technique. That technique is well-established, not least because of extensive history, low cost over the equipment lifetime, the reusability of targets, and the well-known characteristics of the x-ray line radiation that is produced.
Plasma generation of x-rays, by contrast, has not found general acceptance for medical imaging or for other radiological techniques such as the treatment of tumors. This is partly because it is relatively new, but also because equipment is generally expensive, discharge chambers have short lifetimes, and the predominant x-radiation that is produced is not line radiation. However, if plasma x-ray sources could be made more acceptable, they would offer advantages, potentially including greater spatial resolution and lower overall radiation dose, that would give them a role for at least some important applications in radiological medicine.
In the field of radiological treatment of tumors, it has been conventional to use x-rays generated by beam-on-target devices or radiation from radioisotopes. Radioisotope use is also well-established, not least because of extensive history and relatively low cost. However, radiological treatment as currently administered often results in unnecessarily high doses of radiation to the patient.
Thus, there remains a need for adaptations that can make plasma x-ray sources, and possibly other radiation sources, practical as an alternative radiation source for medical and other applications.